MAPREDUCE-3813. Added a cache for resolved racks. Contributed by Vinod K V.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1241209 13f79535-47bb-0310-9956-ffa450edef68

hadoop-mapreduce-project/CHANGES.txt

@@ -713,6 +713,8 @@ Release 0.23.1 - Unreleased
     MAPREDUCE-3810. Performance tweaks - reduced logging in AM and defined
     hascode/equals for ResourceRequest & Priority. (vinodkv via acmurthy) 
 
+    MAPREDUCE-3813. Added a cache for resolved racks. (vinodkv via acmurthy)   
+
 Release 0.23.0 - 2011-11-01 
 
   INCOMPATIBLE CHANGES

hadoop-mapreduce-project/hadoop-yarn/hadoop-yarn-common/src/main/java/org/apache/hadoop/yarn/util/RackResolver.java

@@ -26,6 +26,7 @@
 import org.apache.commons.logging.LogFactory;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.fs.CommonConfigurationKeysPublic;
+import org.apache.hadoop.net.CachedDNSToSwitchMapping;
 import org.apache.hadoop.net.DNSToSwitchMapping;
 import org.apache.hadoop.net.Node;
 import org.apache.hadoop.net.NodeBase;
@@ -50,7 +51,14 @@ public synchronized static void init(Configuration conf) {
     try {
       Constructor<? extends DNSToSwitchMapping> dnsToSwitchMappingConstructor
                              = dnsToSwitchMappingClass.getConstructor();
-      dnsToSwitchMapping = dnsToSwitchMappingConstructor.newInstance();
+      DNSToSwitchMapping newInstance =
+          dnsToSwitchMappingConstructor.newInstance();
+      // Wrap around the configured class with the Cached implementation so as
+      // to save on repetitive lookups.
+      // Check if the impl is already caching, to avoid double caching.
+      dnsToSwitchMapping =
+          ((newInstance instanceof CachedDNSToSwitchMapping) ? newInstance
+              : new CachedDNSToSwitchMapping(newInstance));
     } catch (Exception e) {
       throw new RuntimeException(e);
     }

hadoop-mapreduce-project/hadoop-yarn/hadoop-yarn-common/src/test/java/org/apache/hadoop/yarn/util/TestRackResolver.java

@@ -0,0 +1,71 @@
+/**
+* Licensed to the Apache Software Foundation (ASF) under one
+* or more contributor license agreements.  See the NOTICE file
+* distributed with this work for additional information
+* regarding copyright ownership.  The ASF licenses this file
+* to you under the Apache License, Version 2.0 (the
+* "License"); you may not use this file except in compliance
+* with the License.  You may obtain a copy of the License at
+*
+*     http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+package org.apache.hadoop.yarn.util;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.CommonConfigurationKeysPublic;
+import org.apache.hadoop.net.DNSToSwitchMapping;
+import org.apache.hadoop.net.Node;
+import org.junit.Assert;
+import org.junit.Test;
+
+public class TestRackResolver {
+
+  public static final class MyResolver implements DNSToSwitchMapping {
+
+    int numHost1 = 0;
+
+    @Override
+    public List<String> resolve(List<String> hostList) {
+      // Only one host at a time
+      Assert.assertTrue("hostList size is " + hostList.size(),
+        hostList.size() <= 1);
+      List<String> returnList = new ArrayList<String>();
+      if (hostList.isEmpty()) {
+        return returnList;
+      }
+      if (hostList.get(0).equals("host1")) {
+        numHost1++;
+        returnList.add("/rack1");
+      }
+      // I should not be reached again as RackResolver is supposed to do
+      // caching.
+      Assert.assertTrue(numHost1 <= 1);
+      return returnList;
+    }
+    
+  }
+
+  @Test
+  public void testCaching() {
+    Configuration conf = new Configuration();
+    conf.setClass(
+      CommonConfigurationKeysPublic.NET_TOPOLOGY_NODE_SWITCH_MAPPING_IMPL_KEY,
+      MyResolver.class, DNSToSwitchMapping.class);
+    RackResolver.init(conf);
+    Node node = RackResolver.resolve("host1");
+    Assert.assertEquals("/rack1", node.getNetworkLocation());
+    node = RackResolver.resolve("host1");
+    Assert.assertEquals("/rack1", node.getNetworkLocation());
+  }
+
+}